High density lipoprotein (HDL) levels have been reported to be negatively correlated with risk to atherosclerosis. During investigations of this relationship, we've reported that two non-human primates, the atherosclerosis-susceptible squirrel monkey (Saimiri sciuresus) and the atherosclerosis-resistant cebus monkey (Cebus albifrons) have different lipoprotein responses to saturated fat-induced hypercholesterolemia, i.e., the cebus monkey elevated its HDL levels in contrast to the squirrel monkey which predominately elevated its low density lipoproteins (HDL). We have also reported a higher lecithin-cholesterol acyl transferase activity (LCAT) in the hypercholesterolemic cebus monkey. Utilizing these two monkey species uniquely distinct in their lipoprotein responses to hypercholesterolemia, we proposed to further characterize HDL lipid and apoproteins between the two species to be correlated with HDL size in order to provide a basis for future metabolic studies aimed at measuring HDL synthesis and catabolism as a function of diet and species. By correlating HDL composition and size with expected differences in HDL metabolism as a function of diet and species, it is anticipated that information will be obtainable that will enhance our understanding of the relationship of HDL metabolism and atherosclerosis.